1. Field of the Invention
This invention relates to a measuring apparatus for measuring a characteristic of an object and, particularly to a measuring apparatus which can be suitably set in a specified posture with respect to the object.
2. Description of Related Art
Some measuring apparatuses require adjustment, during a measuring operation, to attain a specified posture with respect to the object. Examples of these apparatuses are listed below.
In recent years, metallic coating and mica coating have been increasingly used as particularly seen in automotive vehicles. Since these metallic materials display different colors depending upon the angle of observation, it is necessary to accurately determine the color of the surface while observing from various angles. There are known goniocolorimeters and multi-angle colorimeters in which light is projected from one light projector and received at a plurality of angles or light is projected from a plurality of angles and received by one photosensor. With the colorimeters of this type, there exist two kinds of lights: the light diffused and reflected by the surface of the object and the light specularly reflected by metallic particles on the surface layer. Accordingly, a projection angle and a reception angle of the light are a key to colorimetry. Thus, it is particularly necessary to accurately set these angles. It has been a general practice that operators bring the colorimeter into contact with the object on the basis of their own judgments. There have been used non-contact type measuring apparatuses in a production line. The measuring apparatuses of this type are fixed and their posture is adjusted basically by displacing the object.
Japanese Unexamined Patent Publication No. 2-245623 discloses a colorimeter which adapts an apparatus fixing foot member including a magnet for magnetic objects to be measured so as to stabilize the posture of the apparatus with respect to the object using magnetic attraction.
Since the colorimetry requires considerably accurate angle setting as described above, it is difficult to obtain data having good reproducibility according to the conventional posture adjusting method which is performed on the basis of the operator's own judgment. Particularly, it is thought to be almost impossible to accurately adjust the posture of the measuring apparatus with respect to an object having a curved surface. Further, the conventional posture adjustment in the production line requires a belt conveyor for moving the object and the object also needs to be positioned with high accuracy. Thus, a control is not easy. Colorimeters including one light projector and one photodetector for determining the color of the normal object which is not coated with a metallic paint has a similar problem of being unable to obtain reproducible data due to a shift in a direction of specular reflection, if their position relative to the object is not fixedly set.
As for the colorimeter disclosed in the above publication, the posture thereof may be stabilized to a certain degree when the object is of magnetic material and has a flat measurement surface. It is impossible to, depending upon the material of the object and the curved shape of its measurement surface, set the colorimeter in a specified posture so as to obtain data having good reproducibility. Thus, the posture adjustment is obliged to largely depend upon the operators' skills and requires a long time, presenting a problem in terms of efficiency.
Further, the accurate posture adjustment of a measuring apparatus with respect to the object is necessary not only for the aforementioned colorimeters, but also for glossimeters for measuring the gloss of an object and densitometers for measuring the concentration. However, these apparatuses also face the problem of impossibility to set them in a specified posture so as to obtain data having high reproducibility if the posture thereof is adjusted on the basis of the operator's judgment.